Definitely nix the molasses.
Genetics and light. If you were giving 35-40ish DLI, then it was genetics. If you were giving as little as 25ish DLI, it might be weak light or genetics. if not going over 30C by quite a bit, probably not the heat. I haven't grown many autos, but the ones i have are not as often dense buds. that could be a small sample error.